1. Field of the Invention
The present invention relates generally to spectroscopy and, more particularly, to the mounting and protective storage of beam splitters which are utilized in a Fourier transform infrared spectrometer.
2. Description of the Prior Art
Fourier transform infrared (FT-IR) spectrometers are widely used in the analysis of chemical compounds. By measuring the absorption of infrared radiation by an unknown sample at various wavelengths in the infrared spectrum, and comparing the results with known standards, these instruments permit considerable useful information concerning the chemical makeup of the unknown sample to be obtained.
In a typical FT-IR spectrometer, infrared radiation from an infrared emitting source is collected and directed through a series of mirrors or other focusing elements to an interferometer which includes a beam splitter that splits the infrared radiation into two separate beams. The two separate beams are then directed to two mirrors which reflect the beams back to the beam splitter where the two beams are spatially recombined into a composite beam that exits the interferometer and is eventually transmitted through or reflected from the sample to be analyzed, and finally brought to focus on an infrared detector. The interferometer system, in combination with the sample, modulates the intensity of the infrared radiation that impinges on the detector, and thereby forms a time variant intensity signal. The output of the detector is digitized and processed in a computer in a conventional manner to yield the desired spectral information.
It is critical to the proper performance of these instruments that the beam splitter be mounted accurately in position within the interferometer so that the infrared radiation is properly split and recombined. Deviations in the position of the beam splitter can produce small errors in the time-domain interferogram which may translate into large errors in the frequency-domain spectrum. Additionally, the beam splitter used in an FT-IR instrument is the most delicate item in the instrument. It is desirable that the beam splitter be protected from handling by the user whenever the beam splitter is placed within or removed from the interferometer. If the user were to touch the beam splitter itself, the beam splitter could be ruined. The most common beam splitters are made of hygroscopic materials. It therefore is important to protect the beam splitter from both moisture and dust. Desiccant materials such as molecular sieve or silica gel may be used to afford additional protection from moisture. It also is desirable that beam splitters, which are not being used be stored in a safe, dry place.